是否可以使用Go通过Unix域套接字发送和接收文件描述符？

Question

In the unix(7) man page for Unix domain sockets, it says that sendmsg can be used with the SCM_RIGHTS flag to send file descriptors over these sockets. Is this supported in Go? Is there any good example code out there showing how it's done?

It appears that there is a Msghdr structure declared in the syscall package. But no functions take it. Maybe I have to use the raw system call interface?

Answer 1

There's a package that does it here: https://github.com/ftrvxmtrx/fd/blob/master/fd.go. However that's using the Syscall package to achieve it. I'm not sure if there's a way to do this with Go standard library API.

In the syscall package, the things to look at are UnixRights, ParseUnixRights, and ParseSocketControlMessage. These can be used in conjunction with Readmsg and Sendmsg to send file descriptors over AF_UNIX sockets.

The basic structure goes something like this for receiving:

buf := make([]byte, syscall.CmsgSpace(<number of file descriptors expected> * 4))
_, _, _, _, err = syscall.Recvmsg(socket, nil, buf, 0)
if err != nil {
    panic(err)
}
var msgs []syscall.SocketControlMessage
msgs, err = syscall.ParseSocketControlMessage(buf)
var allfds []int
for i := 0, i < len(msgs) && err == null; i++ {
    var msgfds []int
    msgfds, err = syscall.ParseUnixRights(&msgs[i])
    append(allfds, msgfds...)
}

And for sending, it's much simpler (var fds []int):

rights := syscall.UnixRights(fds...)
err := syscall.Sendmsg(socket, nil, rights, nil, 0)